EP2122263A1

EP2122263A1 - Method for controlling compressor of air conditioner

Info

Publication number: EP2122263A1
Application number: EP08723021A
Authority: EP
Inventors: Jin-Ha Choi; Il-Nahm Hwang; Won-Chul Kang; Kyung-Won Seo; Chi-Woo Song; Ho-Jong Jeong; Seung-Yong Chang; Tae-Hee Kwak
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2007-03-13
Filing date: 2008-02-20
Publication date: 2009-11-25
Also published as: WO2008111737A1; EP2122263A4; KR101290964B1; KR20080083895A

Abstract

Provided is a method for controlling a compressor of an air conditioner. A constant-speed compressor and an inverter compressor are provided in an outdoor unit, and a plurality of indoor units are connected to the outdoor unit. The constant-speed compressor is driven at a proper time by rapidly detecting a case where the inverter compressor reaches the maximum frequency but fails to satisfy a target pressure.

Description

METHOD FOR CONTROLLING COMPRESSOR OF AIR CONDITIONER

Technical Field

[1] The present disclosure relates to a method for controlling a compressor of an air conditioner. Background Art

[2] In general, an air conditioner performs a cooling operation or a heating operation by circulating coolant through a compressor, a condenser, an expansion unit, and an evaporator. An outdoor heat exchanger and an indoor heat exchanger serve respectively as the condenser and the evaporator in the cooling operation, while the outdoor heat exchanger and the indoor heat exchanger serve respectively as the evaporator and the condenser in the heating operation.

[3] Recently, multi-type air conditioners are widely used to cool/heat a plurality of spaces while providing a large cooling/heating capacity.

[4] A multi-type air conditioner is constructed to include an outdoor unit and a plurality of indoor units connected to the outdoor unit. The outdoor unit has an inverter compressor with a variable speed and a constant- speed compressor with a constant speed.

[5] Thus, the inverter compressor operates solely or in conjunction with the constant- speed compressor, depending on the required cooling/heating capacity.

[6] In a related art multi-type air conditioner, an inverter compressor is driven corresponding to a variable cooling/heating load. In detail, a main controller determines a target frequency, and an inverter controls an operation of the inverter compressor according to the target frequency received from the main controller. Thereafter, when the current frequency of the inverter compressor becomes equal to the target frequency, the main controller determines a new target frequency. If the inverter compressor reaches the maximum frequency but fails to satisfy a target pressure, a constant-speed compressor is driven after reduction of the frequency.

[7] However, if the inverter compressor fails to reach the maximum frequency due to lack of the capacity of the inverter, because there is no means to detect such a case, the main controller cannot drive the constant- speed compressor at a proper time, thus failing to rapidly cope with a load change. Disclosure of Invention Technical Problem

[8] Embodiments provide a method for controlling a compressor of an air conditioner, which drives a constant-speed compressor at a proper time by rapidly detecting a case where an inverter compressor reaches the maximum frequency but fails to satisfy a target pressure. Technical Solution

[9] In one embodiment, a method for controlling a compressor of an air conditioner includes: driving an inverter compressor by selection of an operating mode; transmitting a target frequency of the inverter compressor according to a desired temperature from a controller to an inverter; applying a current corresponding to the target frequency to the inverter; determining, by the inverter, whether the inverter compressor is overloaded according to the target frequency; and determining whether to drive a constant-speed compressor, according to whether the inverter compressor is overloaded.

[10] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

Advantageous Effects

[11] A method for controlling a compressor of an air conditioner according to an embodiment drives a constant- speed compressor at a proper time by rapidly detecting a case where an inverter compressor reaches the maximum frequency but fails to satisfy a target pressure, thereby enhancing the cooling/heating capability.

[12] Also, the compressor is driven to rapidly cope with a load change, thereby increasing the product reliability. Brief Description of the Drawings

[13] Fig. 1 is a block diagram of a multi-type air conditioner according to an embodiment.

[14] Fig. 2 is a block diagram of a system for controlling a compressor according to an embodiment.

[15] Fig. 3 is a flowchart illustrating a method for controlling the compressor according to an embodiment.

[16] Fig. 4 is a graph showing a frequency change of the compressor resulting from the compressor controlling method according to an embodiment. Best Mode for Carrying Out the Invention

[17] Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings.

[18] Fig. 1 is a block diagram of a multi-type air conditioner according to an embodiment.

[19] Referring to Fig. 1, a multi-type air conditioner 10 includes a compressor 11 for compressing coolant, an outdoor heat exchanger 15 serving as a condenser in a cooling mode, an indoor heat exchanger 13 serving as an evaporator in the cooling mode, an expansion unit 14 for expanding coolant having passed through the condenser into a low-temperature low-pressure state, a gas-liquid separator 16 provided at an inlet of the compressor 11 to separate gaseous coolant from liquid coolant, a 4- way valve 12 provided at an outlet of the compressor 11 to switch a flow of coolant to the outdoor heat exchanger 15 or the indoor heat exchanger 13 according to the operating mode, and a controller 17 for controlling the operation of the compressor 11, the operation of the expansion unit 14, and the operation of the 4- way valve 12.

[20] The compressor 11 includes an inverter compressor 112 and a constant- speed compressor 111. The inverter compressor 112 changes in speed according to a load change, while the constant- speed compressor 111 rotates at a constant speed. Two ore more indoor heat exchangers 13 are connected in parallel and are installed independently in separate spaces. The outdoor heat exchanger 15, the compressor 11, and the gas-liquid separator 16 are disposed in an outdoor unit, while the indoor heat exchanger 13 is disposed in an indoor unit. The expansion unit 14 is disposed in the outdoor heat exchanger 15 of the indoor heat exchanger 13 depending on the product type.

[21] Hereinafter, a cooling operation of the above multi-type air conditioner will be described as an example.

[22] When a cooling mode is selected, the inverter compressor 112 is driven to compress coolant into a high-temperature high-pressure state. Thereafter, the compressed coolant flows through the 4- way valve 12 into the outdoor heat exchanger 15. Thereafter, the coolant passing through the outdoor heat exchanger 15 changes into a high- temperature liquid coolant by heat exchange with the external air. Thereafter, the coolant having passed through the outdoor heat exchanger 15 changes into a low- temperature low-pressure 2-phase coolant while passing through the expansion unit 14. Thereafter, the coolant having passed through the expansion unit 14 flows into the indoor heat exchanger 13. Thereafter, the coolant flowing through the indoor heat exchanger 13 changes into a low-temperature gaseous coolant by heat exchange with the indoor air. This process cools the indoor air down to a predetermined temperature. Thereafter, the coolant having passed through the indoor heat exchanger 13 flows through the 4-way valve 12 into the gas-liquid separator 16. Thereafter, only the gaseous coolant separated from the liquid coolant by the gas-liquid separator 16 flows into the compressor 11.

[23] At this point, in the mode of driving only the inverter compressor 112, all the coolant having passed through the gas-liquid separator 16 flows into the inverter compressor 112. If a cooling load increases, the controller 17 controls the inverter compressor 112 to be driven in conjunction with the constant-speed compressor 111.

[24] Fig. 2 is a block diagram of a system for controlling the compressor 11 according to an embodiment.

[25] Referring to Fig. 2, a target frequency is transmitted from the controller 17 to an inverter 19 and a current corresponding to the target frequency is transmitted from a power unit 18 to the inverter 19. The inverter 19 controls the inverter compressor 112 to be driven at the target frequency. If a load change necessitates driving the constant- speed compressor 111, the controller 17 turns on a switch 20 that connects the constant-speed compressor 111 and the power unit 18. Then the power output from the power unit 18 is distributed to the inverter 19 and the constant-speed compressor 11 such that the inverter compressor 112 and the constant-speed compressor 111 are driven simultaneously. At this point, the target frequency of the inverter compressor 112 decreases because the constant- speed compressor 111 is driven in conjunction with the inverter compressor 112.

[26] Hereinafter, a method for controlling the constant- speed compressor and the inverter compressor will be described in detail with reference to Fig. 3.

[27] Fig. 3 is a flowchart illustrating a method for controlling the compressor according to an embodiment.

[28] Hereinafter, a case where the multi-type air conditioner operates in a cooling mode will be described as an exemplary embodiment.

[29] Referring to Fig. 3, a cooling mode is selected by a user in step S 110. If a desired indoor temperature is input in step S 120, the inverter compressor is driven in step S 130. In step S 140, an indoor temperature is detected by a temperature sensor (not illustrated) installed in the air conditioner. In step S 150, the controller 17 determines whether the detected temperature is lower than or equal to the input temperature.

[30] If the detected temperature is lower than or equal to the input temperature (in step

S 150), the compressor stops in step S 160. On the other hand, if the detected temperature is higher than the input temperature (in step S 150), the controller 17 transmits a target frequency N for driving the compressor to the inverter 19 in step S 151.

[31] In step S 152, the power unit 18 provides a current corresponding to the target frequency N to the inverter 19.

[32] In step S 153, the inverter 19 determines whether the provided current exceeds the allowable current of the inverter 19. If the provided current exceeds the allowable current (in step S 153), the inverter 19 transmits an overload signal to the controller 17 in step S154. In step S155, the controller 17 determines whether there is a constant- speed compressor that can be driven. If there is no constant- speed compressor that can be driven (in step S 155), the controller 17 controls the inverter compressor to be driven at the maximum possible frequency in step S 159.

[33] On the other hand, if there is a constant- speed compressor that can be driven (in step

S 155), the controller 17 drives the constant-speed compressor while reducing the target frequency, in step S 157. Herein, the range of reducing the target frequency is expressed as the following equation.

[34]

[35] F_c = F_r - F_p

[36] F_c: the range of reducing the target frequency.

[37] F_r: the frequency corresponding to the required capacity or load of the compressor.

[38] F_p: the frequency corresponding to the possible capacity or load of the constant-speed compressor.

[39]

[40] For example, if the required capacity of the compressor is 100 and if the possible capacity of the constant- speed compressor is 60, the driving frequency of the inverter compressor becomes a frequency corresponding to a compressing capacity of 40. That is, the controller 17 reduces the target frequency to the extent that the inverter compressor can exhibit a compressing capacity of 40, and transmits the reduced target frequency to the inverter 19.

[41] In step S 158, the controller 17 determines in real time whether an indoor temperature, which is detected by the temperature sensor while the constant- speed compressor and the inverter compressor are driven simultaneously, is lower than or equal to a desired input temperature. If the detected temperature is lower than or equal to the input temperature (in step S 158), the inverter compressor and the constant-speed compressor stop operating in step S 160. On the other hand, if the detected temperature is higher than the input temperature (in step S 158), the inverter compressor and the constant-speed compressor continue to operate.

[42] On the other hand, if the provided current corresponding to the target frequency is lower than or equal to the allowable current (in step S 153), the controller 17 increases the speed of the inverter compressor until the driving frequency of the inverter compressor reaches the target frequency, in step S 170. If the driving frequency of the inverter compressor reaches the target frequency in step S 171, the controller 17 increases the target frequency N in step S 172. Thereafter, an indoor temperature is detected by the temperature sensor. If the detected temperature is still higher than the input temperature, the controller 17 repeats the step S 151 of driving the inverter compressor at the increased target frequency.

[43] Fig. 4 is a graph showing a frequency change of the compressor resulting from the compressor controlling method according to an embodiment.

[44] In Fig. 4, an X-axis represents an elapse time and a Y-axis represents the driving frequency of the inverter compressor.

[45] In order to reduce the indoor temperature to the input temperature, the controller 17 transmits the target frequency to the inverter to increase the driving frequency of the inverter compressor.

[46] To this end, the controller increases the target frequency gradually, instead of setting the target frequency to the maximum value from the beginning. That is, the controller transmits the target frequency of a predetermined value so that the inverter compressor reaches a predetermined target frequency. If the inverter compressor reaches the predetermined target frequency, the controller increases the speed of the inverter compressor by increasing the target frequency above a predetermined level. If the inverter compressor reaches the maximum frequency but fails to satisfy the target frequency, the inverter transmits an overload signal to the controller. Then, the controller drives the constant- speed compressor while reducing the target frequency of the inverter compressor.

[47] As described above, the present invention can prevent the inverter compressor from operating in an overload state, thereby increasing the lifetime of the compressor

[48] Also, the present invention drives the constant-speed compressor by rapidly detecting the overload of the inverter compressor, thereby performing the cooling/heating operation stably.

[49] Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Claims

[1] A method for controlling a compressor of an air conditioner, comprising: driving an inverter compressor by selection of an operating mode; transmitting a target frequency of the inverter compressor according to a desired temperature from a controller to an inverter; applying a current corresponding to the target frequency to the inverter; determining, by the inverter, whether the inverter compressor is overloaded according to the target frequency; and determining whether to drive a constant- speed compressor, according to whether the inverter compressor is overloaded. [2] The method according to claim 1, wherein the target frequency increases gradually till the earlier of the time when an indoor temperature reaches a target temperature and the time when the inverter compressor is driven at the maximum frequency. [3] The method according to claim 1, wherein whether the inverter compressor is overloaded is determined by comparing the value of the allowable current of the inverter and the value of the current applied to the inverter according to the target frequency. [4] The method according to claim 1, wherein, if the inverter compressor is overloaded according to the target frequency, an overload signal is transmitted from the inverter to the controller and whether to drive the constant- speed compressor is determined according to the overload signal. [5] The method according to claim 4, wherein the determining of whether to drive the constant-speed compressor determines whether there is a constant-speed compressor that can be driven. [6] The method according to claim 5, wherein the inverter compressor continues to be driven at the maximum possible frequency if there is no constant-speed compressor that can be driven. [7] The method according to claim 5, wherein, if there is a constant-speed compressor that can be driven, the driving frequency of the inverter compressor is reduced while driving the constant- speed compressor. [8] The method according to claim 7, wherein the driving frequency of the inverter compressor is reduced by a target signal reduction signal received from the inverter.